Side light emitting type semiconductor laser diode having dielectric layer formed on active layer

ABSTRACT

Provided is a side light emitting type semiconductor laser diode in which a dielectric layer is formed on an active layer. The side light emitting type semiconductor laser diode includes an n-clad layer, an n-light guide layer, an active layer and a p-light guide layer sequentially formed on a substrate, and a dielectric layer with a ridge structure formed on the p-light guide layer.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No.10-2005-0096159, filed on Oct. 12, 2005, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to a semiconductor layer diode, and moreparticularly, to a side light emitting type semiconductor laser diodeincluding a dielectric layer formed on an active layer, and ap-conductive layer supplying current to both sides of the dielectriclayer and a method of manufacturing the same.

2. Description of the Related Art

Semiconductor laser diodes, currently used in light sources of variousinformation processing apparatuses, require high light extractionefficiency versus an applied electric power to increase informationdensity. Accordingly, research into the optimization of the structure ofa laser diode has been conducted.

FIG. 1 is a cross-sectional view of a conventional semiconductor laserdiode. Referring to FIG. 1, an n-AlGaN layer 11 is formed on a substrate10 and an n-AlGaN clad layer 12, an InGaN active layer 13 having a MultiQuantum Wall (MQW) structure, a p-AlGaN clad layer 14, a p-contact layer15 and a p-electrode layer 16 are sequentially formed on the n-AlGaNlayer 11. In addition, an n-electrode layer 17 is formed on the regionof the n-AlGaN layer 11 in a region where the n-AlGaN clad layer 12 isnot formed.

In order to form the semiconductor laser diode illustrated in FIG. 1,the n-AlGaN clad layer 12, the InGaN MQW active layer 13, the p-AlGaNclad layer 14, the p-contact layer 15 and the p-electrode layer 16 aresequentially formed on the n-AlGaN layer 11. Then, semiconductormaterials are removed from the region of the n-AlGaN layer 11 where then-electrode layer 17 is to be formed to expose the n-AlGaN layer 11, andthen the n-electrode layer 17 is formed.

The conventional semiconductor laser diode illustrated in FIG. 1 has thefollowing problems.

First, in the process of forming the semiconductor laser diode shown inFIG. 1, while heat-treatment of the p-AlGaN clad layer 14 is performedat a high temperature in a growth process, segregation of indium (In)grown at a low temperature is performed in the InGaN active layer 13 andthus, the quality of the MQW structure of the InGaN active layer 13 maydecline.

Second, doping materials using p-type impurities, for example, Mg, maycause a lattice defect of the p-AlGaN clad layer 14, and thus opticalloss is increased.

Third, due to diffusion of Mg in the p-AlGaN clad layer 14, the qualityof the MQW structure in the InGaN active layer 13 may decline.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a semiconductor laser diode having adielectric layer instead of a p-clad layer formed on an active layer toimprove optical characteristics of the semiconductor laser diode.

According to an aspect of the present disclosure, there is provided aside light emitting type semiconductor laser diode including: asubstrate; an n-clad layer disposed on the substrate; an n-light guidelayer disposed on the n-clad layer; an active layer disposed on then-light guide layer; a p-light guide layer disposed on the active layer;and a dielectric layer with a ridge structure disposed on the p-lightguide layer.

A p-contact layer may be interposed between the p-light guide layer andthe dielectric layer.

A p-electrode layer may be disposed on the sides of the dielectriclayer.

An n-semiconductor layer may be interposed between the substrate and then-clad layer and an n-electrode layer may be disposed on one portion ofthe n-semiconductor layer.

A current restriction region may be disposed on both sides of thep-light guide layer.

A current restriction region may be disposed on the upper surface of then-light guide layer to restrict a current applied to the active layer.

A current diffusion layer may be interposed between the p-light guidelayer and the p-contact layer.

The n-clad layer may be formed of Al_(x)GaN(x≧0). The n-light guidelayer may be formed of In_(x)GaN(x≧0). The active layer may have a MultiQuantum Wall (MOW) structure formed of In_(x)GaN (x≧0). The p-lightguide layer may be formed of In_(x)GaN(x≧0).

The dielectric layer may include at least one material selected from thegroup consisting of SiO₂, SiN_(x), HfO_(x), AlN, Al₂O₃, TiO₂, ZrO₂, MnO,and Ta₂O₅.

The p-contact layer may be formed of In_(x)GaN(x≧0).

The current restriction layer may be formed of one of undoped-AlGaN andp-AlGaN and the current diffusion layer may be formed of AlGaN.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present disclosurewill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view of a conventional semiconductor laserdiode;

FIG. 2 is a cross-sectional view of a semiconductor laser diode having adielectric layer formed on an active layer according to an embodiment ofthe present disclosure;

FIG. 3A is a cross-sectional view of a laser diode according to anembodiment of the present disclosure in which a current restrictionregion is formed on a p-light guide layer;

FIG. 3B is a cross-sectional view of a laser diode according to anembodiment of the present disclosure in which a current restrictionlayer is formed on the structure illustrated in FIG. 3A;

FIG. 4 is a cross-sectional view of a laser diode including a currentdiffusion layer on the p-light guide layer in the basic structureillustrated in FIG. 2;

FIG. 5 is a graph of the result of a simulation showing an overlappingratio of a dielectric layer and a laser light mode oscillating in anactive layer of the semiconductor laser diode of an embodiment of thepresent disclosure and a p-clad layer and a laser light mode oscillatingin an active layer of a conventional semiconductor laser diode; and

FIG. 6 is a graph of modal loss according to ridge width of a dielectriclayer having a ridge structure in a semiconductor laser diode accordingto an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure will now describe more fully, with reference tothe accompanying drawings, exemplary embodiments of the disclosure. Theclaimed invention may, however, be embodied in many different forms andshould not be construed as being limited to the embodiments set forthherein; rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the concept of theinvention to those skilled in the art. In the drawings, the thicknessesof layers and regions are exaggerated for clarity. Like referencenumerals in the drawings denote like elements, and thus theirdescriptions will not be repeated.

FIG. 2 is a cross-sectional view of a side light emitting typesemiconductor laser diode in which a dielectric layer 27 is formed on anactive layer according to an embodiment of the present disclosure.

Referring to FIG. 2, an n-semiconductor layer 21 is formed on asubstrate 20 and an n-clad layer 22, an n-light guide layer 23, anactive layer 24 and a p-light guide layer 25 are sequentially formed onthe n-semiconductor layer 21. Optionally, a p-contact layer 26 can befurther formed on the p-light guide layer 25. In addition, thedielectric layer 27 is formed on a central region of the p-light guidelayer 25 or the p-contact layer 26, and a p-electrode layer 28 is formedat the sides of the dielectric layer 27. An n-electrode layer 29 isformed on the remaining portion of the n-semiconductor layer 21 wherethe n-clad layer 22 is not formed.

The n-semiconductor layer 21 and the n-clad layer 22 can respectively beformed of Al_(x)GaN (x≧0). The n-light guide layer 23 can be formed ofIn_(x)GaN (x≧0) and the active layer 24 can have a Multi Quantum Wall(MQW) structure and be formed of In_(x)GaN (x≧0). The p-light guidelayer 25 can be formed of In_(x)GaN(x≧0) and the p-contact layer 26 canbe formed of In_(x)GaN(x≧0).

In an embodiment of the present disclosure, the dielectric layer 27 hasa ridge structure on the p-light guide layer 25 or the p-contact layer26, and is formed of a dielectric material such as SiO₂, SiN_(x),HfO_(x), AlN, Al₂O₃, TiO₂, ZrO₂, MnO or Ta₂O₅. The dielectric layer 27plays a role in guiding the light mode generated in the active layer 24by the current supplied to the p-electrode layer 28 and the n-electrodelayer 29. In order to oscillate the laser, the current supplied to theactive layer 24 is supplied through the p-electrode layer 28 formed onboth sides of the dielectric layer 27.

To increase the efficiency of the supply of current, a currentrestriction region can be formed on the p-light guide layer 25 or then-light guide layer 23. This is described below with reference to FIGS.3A through 3B.

FIG. 3A is a cross-sectional view of a laser diode according to anembodiment of the present disclosure in which current restrictionregions 25 a are formed in the p-light guide layer 25. Referring to FIG.3A, the n-semiconductor layer 21 is formed on the substrate 20 and then-clad layer 22, and the n-light guide layer 23, the active layer 24 andthe p-light guide layer 25 are sequentially formed on then-semiconductor layer 21. Optionally, the p-contact layer 26 can befurther formed on the p-light guide layer 25. In addition, thedielectric layer 27 is formed on the central region of the p-light guidelayer 25 or the p-contact layer 26, and the p-electrode layer 28 isformed at the sides of the dielectric layer 27. The n-electrode layer 29is formed on the remaining portion of the n-semiconductor layer 21 wherethe n-clad layer 22 is not formed. The structure herein is the same asthe basic structure illustrated in FIG. 2. However, in FIG. 3A, thecurrent restriction regions 25 a are further formed in the p-light guidelayer 25.

The current restriction regions 25 a are formed by injecting a materialsuch as H, B or NH₃ into both sides of the p-light guide layer 25 usingimplantation when the p-light guide layer 25 is formed. When the p-lightguide layer 25 is optionally formed, p-type impurities can be doped inthe region excluding the current restriction regions 25 a. Thus, if thecurrent is supplied through the p-contact layer 28 formed on both sidesof the dielectric layer 27, the current passes through a space betweenthe current restriction regions 25 a of the p-light guide layer 25,instead of through the current restriction regions 25 a themselves, andthen reach the active layer 24. Consequentially, the current is mainlysupplied to the central region of the active layer 24, and thusefficient laser oscillation can occur.

Moreover, if the current restriction regions 25 a are formed on bothportions of the n-light guide layer 23, the current can be suppliedmainly to the central region of the active layer 24. That is, if thematerial such as H, B or NH₃ is injected into both sides of the p-lightguide layer 25 using implantation, or the n-light guide layer 23 isoptionally formed, n-type impurities can be doped in the regionexcluding the current restriction regions 25 a.

FIG. 3B is a cross-sectional view of a laser diode including a currentrestriction layer 30. Referring to FIG. 3B, the current restrictionlayer 30 is formed between the n-light guide layer 23 and the activelayer 24 to restrict the route of the current supplied from then-electrode layer 29, instead of forming the current restriction regionsin the n-light guide layer 25. In detail, after forming the n-lightguide layer 23, undoped AlGaN or p-AlGaN is supplied to the uppersurface of the n-light guide layer 23 and the n-light guide layer 23 isexposed by etching the central region of the undoped AlGaN or AlGaN.Then, the active layer 24 and the p-light guide layer 25 aresequentially formed on the upper surface of the etched region.Consequently, the active layer 24 is grooved. Accordingly, the currentsupplied by the n-electrode layer 29 cannot pass through the currentrestriction layer 30, and thus the current is supplied mainly to thecentral region of the active layer 24 through the space formed in thecurrent restriction layer 30. Thus, efficient laser oscillation canoccur.

FIG. 4 is a cross-sectional view of a laser diode including a currentdiffusion layer 31 on the p-light guide layer 25 in the basic structureillustrated in FIG. 2.

Referring to FIG. 4, the n-semiconductor layer 21 is formed on thesubstrate 20 and the n-clad layer 22, the n-light guide layer 23, theactive layer 24, the p-light guide layer 25 and the current diffusionlayer 31 are sequentially formed on the n-semiconductor layer 21.Optionally, the p-contact layer 26 can be further formed on the currentdiffusion layer 31. In addition, the dielectric layer 27 is formed onthe central region of the p-light guide layer 25 or the p-contact layer26, and the p-electrode layer 28 is formed at the sides of thedielectric layer 27. The n-electrode layer 29 is formed on the remainingportion of the n-semiconductor layer 21 where the n-clad layer 22 is notformed. The current diffusion layer 31 can be formed of AlGaN, and thecurrent supplied through the p-electrode layer 28 is supplied to theactive layer 24 through the current diffusion layer 31. The currentdiffusion layer 31 is thin (approximately 100 nm), and a process of hightemperature oxidation is either unnecessary or performed for a veryshort time. Accordingly, the quality of the MQW structure in segregationof indium (In) of the active layer 24 may not decline.

Hereinafter, the laser diode of an embodiment of the present disclosureand a conventional laser diode will be compared with reference to FIG.5. FIG. 5 is a graph of the result of a simulation showing anoverlapping ratio of a dielectric layer and a laser light modeoscillating in an active layer of the semiconductor laser diode of anembodiment of the present disclosure and a p-clad layer and a laserlight mode oscillating in an active layer of a conventionalsemiconductor laser diode. In a conventional laser diode, AIGaN is usedfor the p-clad layer and the refractive index of the p-clad layer isabout 2.5. Referring to FIG. 5, when the laser beam that oscillated inthe active layer was transmitted toward the sides of the active layer,the overlapping ratio of the light mode to the p-clad layer, which wasdoped with Mg as a p-type impurity, was over 20%, and thus optical losswas low.

In addition, in the laser diode structure illustrated in FIG. 3A, theoverlapping ratio of the dielectric layer to the laser oscillated in theactive layer was investigated by using materials with differentrefractive indexes to form the dielectric layer. It was found that theoverlapping ratio was less than 10% even when the dielectric layer wasformed of a material with a refractive index of 2.5. Consequently, thelaser diode structure of an embodiment of the present disclosure showeda greater decrease in optical loss than that of the conventional art.

FIG. 6 is a graph of modal loss according to ridge width of a dielectriclayer having a ridge structure in a semiconductor laser diode accordingto an embodiment of the present disclosure. FIG. 6 shows the results fora fundamental mode (0^(th) mode) and a 1st-order mode of an oscillatedlaser. In the semiconductor laser diode according to an embodiment ofthe present disclosure illustrated in FIG. 2, the optical loss occurs inthe p-electrode layer 28, which is formed of a metal material at thesides of the dielectric layer 27 having the ridge structure. When thewidth of the dielectric layer 27 is less than approximately 2 μm, themodal loss of the fundamental mode is small, below 20 cm⁻¹. On the otherhand, since the loss of the 1st-order mode is high, a high kink levelexists due to the efficiency of the mode selection. Thus, the laseroscillated in the active layer can be easily emitted as a singletransverse mode laser.

The semiconductor laser diode of the present disclosure has thefollowing advantages.

First, a characteristic decline of the active layer which may occur inthe growth process of the p-clad layer at a high temperature can beprevented.

Second, optical loss due to diffusion of Mg, the p-type doping material,can be prevented.

Third, the material constituting the dielectric layer can be selectedaccording to its refractive index.

Fourth, using a difference between the optical losses of the fundamentalmode of the oscillated laser in a metal contact and the 1st-order mode,an oscillation of high order mode laser can be controlled.

While the present disclosure has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present disclosure as defined by the following claims.

1-4. (canceled)
 5. A side light emitting type semiconductor laser diodecomprising a substrate; an n-clad layer disposed on the substrate; ann-light guide layer disposed on the n-clad layer; an active layerdisposed on the n-light guide layer; a p-light guide layer disposed onthe active layer; a dielectric layer with a ridge structure disposed onthe p-light guide layer; and a current restriction region disposed onboth sides of the p-light guide layer.
 6. The side light emitting typesemiconductor laser diode of claim 5, further comprising a currentrestriction region disposed on the upper surface of the n-light guidelayer to restrict a current applied to the active layer.
 7. The sidelight emitting type semiconductor laser diode of claim 5, furthercomprising a p-contact layer interposed between the p-light guide layerand the dielectric layer and a current diffusion layer interposedbetween the p-light guide layer and the p-contact layer. 8-13.(canceled)
 14. The side light emitting type semiconductor laser diode ofclaim 6, wherein the current restriction layer is formed of one ofundoped AlGaN and p-AlGaN.
 15. The side light emitting typesemiconductor laser diode of claim 7, wherein the current diffusionlayer is formed of AlGaN.